Hello, below are some suggestions:

1. Ensure that it is the TP-Link login page; you can refer to https://www.tp-link.com/en/faq-712.html to login 

2. Please enter admin and have a try.

3. If failed, please change another web browser or another device to access the web interface again. 

 

May it help.

if the default userid and password does not work, then it is time to reset the router to factory specs. See your router manual or google for your specific model for instructions. After the reset, you will need to reenter all of your configuration data. You should always change the default userid and password for security reasons. If your router is in a secure area, you ca tape the new userid and password to the bottom or back of the router.

Correct, if the default userid and password does not work, need reset to solve it. 

After that, you can login with the default userid and password and you can customize them for security.